Determine the concentration of lime water.

Course work 2

The aim of this experiment is to determine the concentration of the given limewater solution in g dm.

The aim of this experiment is to determine the concentration of the given limewater solution in g dm. 

Assessed Practical

To determine the concentration of a limewater solution

Plan

The aim of this experiment is to determine the concentration of the given limewater solution in g dm. I have the choice of what apparatus I use and also the design of my own experiment. I am provided with the following:

Indicator (Methyl orange)

250cm3 of limewater (which contains approximately 1g dm of calcium hydroxide)

Hydrochloric acid (concentration of 2.00 mol dm ), which is too concentrated and needs to be diluted.

The following list provides information of the equipment, apparatus and chemicals used:

· 250cm3 of limewater

· Hydrochloric acid

· Methyl orange (indicator)

· Distilled water

· Clamp and stand

· White tile

· Burette

· Conical and volumetric flask

· Pipette (25cm3)

Detailed method of procedure used

To start the experiment I firstly need to dilute the Hydrochloric acid. By using a pipette and a flask it is a good way of making sure the experiment is accurate. I need to dilute the acid to 0.125 moles. I achieve this by adding a 50:50 ratio of hydrochloric acid to distilled water. I then place half of this solution into the volumetric flask and again add another 50% distilled water. I measure the amount of water by looking on the graduated marks on the flask. I repeat this procedure 4 times until my target of 0.125 moles is achieved. When you have obtained the correct concentration of Hydrochloric acid you can proceed with the experiment. I set up the following apparatus:

In the flask I have used 25.0cm3 of limewater and a few drops of methyl orange. Obtained by using a pipette. By adding the drops of methyl orange the neutralisation point should be acquired. The solution should turn a light orange and proceed to pink at the end of the experiment.

By slowly adding the acid into the limewater the point where complete reaction occurs is when the indicator changes colour. This is known as the equivalence point. This experiment is then repeated several times in order to gain the necessary reliable results.

My results are as follows:

Average titration = 10.9+11.2+11.1+11.1+10.5= 54.8 54.8¸5=10.96

Balanced equations

In order to achieve limewater we dissolve slaked lime in water to get a solution of calcium hydroxide (Ca (OH) (aq)).

Quicklime + water ® Slaked lime

CaO(s)+H20(I) ® Ca(OH)2(s)

In this reaction it shows how the calcium oxide reacts with water to produce calcium hydroxide. After adding more water to calcium hydroxide it produces the saturated aqueous solution known as Limewater.

In the experiment limewater reacts with hydrochloric acid, to make the concentration of the limewater.

Limewater + Hydrochloric acid ® Calcium chloride + water + Hydrogen

Ca(OH)2(aq)+2HCL ® CaCl2+ 2H20

Calculations

Number of moles of HCL

Number of moles = volume of solution x molarity

1dm3 = 10x10x10cm3 = 1000cm3

10.96 ¸ 1000 x 0.125 = 0.00137 = 1.3 x 10 mol

Concentration of limewater in mol dm3

2(Volume of acid cm3) x Molarity of acid = Volume of alkalai (cm3) x Molarity of alkalai

1000 1000

2 (10.96cm3 x 0.125) = 25cm3 x mo.Ca(OH)2

1000 1000

= 0.00274

Mol. Ca(OH)2 = 0.00274 x 1000 = 0.1096 mol dm3

25

0.1096 x 74.1(Molarmass) = 8.12gdm3

Evaluation

My practical experiment went quite well and I got a variety of results, which were suitable for the task given. My results show that I got two identical results and one just 1.1cm3 off. Which suggests that I have been accurate and precise during the experiment. By being accurate it came about by specific apparatus I used, which restricted errors. However during the experiment I came across an array of errors and circumstances that could have restricted my results. Some of which include Random and systematic errors. Some of the miscalculations I made consist of: -

· Splashes occurring on the flask during titration

· Chemicals carried over to the next experiment

· Colour change not exact

· Measurements not accurate

· Pipette holding back solution

The first error I found was that when I was carrying out the titration process, fractional splashes were occurring on the sides of the flask while the titration was taking place. This could maybe be avoided next time by lowering the burette to the bottom of the flask so hardly any splashes can occur. The pipette that I used was also holding back some of the solution so not all of the solution was transferred. This problem also occurred when measuring the chemicals because some chemicals were carried over to the next experiment. This could be avoided by drying out the beakers and measuring cylinders or by using separate apparatus. A lot of the errors came from measurements because you rely on the human eye. However the measurements were as accurate as possible. The pipette and burette have an accuracy of approximately ±0.05cm3. This is a lot more accurate compared to that of the burette, which has an accuracy of ±5.00cm3. Knowing this information explains how error through equipment is minimal. Also rely on by the human eye would be the judgement of colour change. It's very difficult to get the exact same colour at the end point of the indicator with the naked eye. Which is why I have used 0.125mol dm of Hydrochloric acid because it makes the results easier to counter for.

The experiment can be made better by making sure all the above errors are accurate and improved on. Also doing several more titration experiments will give me more results, which would make my average result better and more precise. If there were a bigger quantity of limewater for the titration it would reduce the percentage error. In some laboratories specific computer software can be used. Certain programs hold information on the previous titration and when the second titration matches the previous; the experiment is automatically stopped. This is a very accurate way of judging the colour change and totally rules out human error.

I think my results are reasonably accurate and fair and I have avoided from making any real big experimental errors.

Course work 3

Aim: The aim of this experiment is it to find out the concentration of Limewater by performing a titration with hydrochloric acid which has concentration exactly 2.00M.. What is required for me is that I have to design my own experiment and chose the right and appropriate apparatus and equipment. I will be provided with 250cm3 of limewater, which has been made to which contains approximately 1g/dm3 of calcium Hydroxide.

We were also give Hydrochloric acid (HCl) with a concentration of 2.00 mol/dm3 normal laboratory apparatus was also given and so was an indicator.

Introduction into Limestone

Limestone and chalk are used in large quantities to manufacture quicklime and cement. Strong heating of calcium carbonate produces calcium oxide, CaO, and carbon dioxide.

CaCO3(s) ࠃaO (s) + CO2 (g)

Limestone is given the equation CaO, slaked lime is produced when CaO reacts with water, this is where further amount of H2O is added which turns this into a saturated aqueous solution known as limewater. Ca(OH)2 (aq) and is used for tests to show the presence of CO2.

I will be carrying out a titration method to fin out the exact concentration of limewater. I find that this will be a more reliable and accurate way of obtaining my results.

A titration method will give me the precise endpoint of the reaction, which will give me the concentration of limewater in the conical flask.

To obtain best results and for my whole experiment to be reliable, I will be repeating the experiment three times, and recording the average reading.

Theory Of Experiment

This reaction that I ill do for my experiment will take place as the limewater in the volumetric flask reacts with the hydrochloric acid. The equation is as follows.

Ca(OH)2(aq) + 2HCL(aq) ࠃaCl (l) + 2H2O (l)

The mole ration of the above reaction of calcium hydroxide and hydrochloric acid is a ration of 2:1

Ca(OH)2 : HCl

2 : 1

In order for me to carry out my experiment and for it to be accurate and reliable, it will be necessary to dilute the HCl acid.

It is in my knowledge that a concentration of about 0.01mol/dm3 would enable me to achieve reliable results.

To find out exactly how much I have to dilute the HCl I will have to find out the number of moles of CaO(OH)2.

The mass of CaO(OH)2 is 1g/dm3, to work out the moles I have to use this formula.

Number of moles Mass

Mr

Mr of CaO(OH)2 = 40.1 + (1x2) + (16x2) = 74.1

Now divide it with the mass 1.00

74.1 =0.013495276

I will now divide the HCl by 100 so it will be close to the number of moles of CaO(OH)2.

The dilution factor 2.00mol/dm3

100 = 0.02 mol/dm3

doing this will mean that the concentration of HCl is 100 times smaller because of the division I have made above. When I obtain my results at the end I will multiply it to 100.

Limewater consists of distilled water and calcium hydroxide. This is an aqueous solution. In my experiment I will be titrating a sample of limewater with hydrochloric acid in order to find the concentration of the limewater.

The general equation for a neutralisation reaction is:

Acid + Metal Hydroxide ͥtal Salt + Water

Reducing Errors

Accuracy is very important in this experiment, as accurate results need to be recorded from the burette, as the results are needed to work out calculations of the concentration of the limewater. This means that as many measures as possible need to be taken, to make the results as accurate as possible. It is very important to use the most appropriate equipment available for use. This is why I have chosen to use a pipette, volumetric flask and a burette, as they have an accuracy of +-0.005 cm, which should produce a suitable accuracy for my experiment. It is very important to read of the burette as accurately as possible and to make sure that the reading is taken from the bottom of the meniscus. This is why it is helpful to have a piece of white paper behind where you are trying to read on the burette, so it is clearer to seethe bottom of the meniscus. It will be necessary to wash out some of the equipment when I am using it so I can repeat the titration to get concordant results. Some of the equipment will need to be washed out with a particular solution. For instance when washing out the burette you must wash it out with the hydrochloric acid solution, as if you washed it out with water it would affect the results as it would further dilute the hydrochloric acid which was going to be put in there. When running off the hydrochloric acid into the conical flask it is necessary to be very accurate, right to the last drop, so that you reach the endpoint and are not under it, or overshoot it

, choosing a suitable indicator is also important, I had to be extremely careful with this, I have chosen to use the indicator methyl orange. The limewater used will be a relatively weak base so it will be appropriate for using methyl orange, as it has an end point on the scale between 8-5. Other indicators can give wrong readings such as phenolphthalein indicator; this has an end point, which is much higher up the scale. If phenolphthalein is used the end point would be reached before the equivalence point.

To find out the percentage of an error the equation below can be used

Total Error 0.10

Titre X100 = Titre X100

Safety Procedures

Safety is very important and it is necessary to follow safety procedures when doing any experiment. Eye protection must be worn such as goggles, not following this safety rule may result in hazardous chemicals contacting with the skin or eyes. Long hair and objects must be tied back. Extra care should be taken because of the corrosive chemicals, which you are working around such as HCL. A lab coat should also be worn in case any spillage falls onto your clothes.

To avoid any accidents the apparatus should be set up correctly, it should also be set up in a suitable place such as the middle of the lab table.

The solutions should be labelled correctly and the lids of the solutions should are placed on the right bottles and should be secured tightly on

Its important to use the minimum and only required amounts of the solution, this is done to avoid spillages and the waste of the chemicals.

All the apparatus should be securely fastened into place such as the burette attached to the clamp, and the clamp to the stand. The chemicals that we will use are limewater and hydrochloric acid and the hazards are as follows:

• Hydrochloric acid - Very corrosive, irritant.
• Limewater (alkali) - Irritant.

The reaction between the hydrochloric acid and limewater will also produce calcium chloride and water both of which have no hazards and are not dangerous at all. Phenolphthalein, which will be used as well, has no dangers to health and will not react with any of the other chemicals to produce anything dangerous. Also any reaction involving HCl can often be quite violent so great care must be taken however this is not expected with this particular experiment.

Apparatus

Limewater solution, 250 cm3

Hydrochloric Acid, 25 cm3

Conical Flask, 250 cm3

Volumetric Flask 100cm3

Burette 25cm3

Pipette

Indicator methyl orange

Distilled water

Funnel

Clamp and Stand

White Tile

Method

Before staring the experiment the hydrochloric acid must be diluted.

Make sure the burette is clean and double check by rindsing it out with ditilled water two to three times, get rid of the excess water by pouring it down the sink.

· Measure out exactly 2.00cm3 of HCl by the burette by placing the bottom of the meniscus exactly on the 2.00 mark to obtain accurate results.

· Rinse out the conical flask with distilled water two to three times and remove the excess water; fill the conical flask with 200cm3 of distilled water.

· Add the HCl to the distilled water, and now the HCl has been diluted.

Titration

· wash all equipment with distilled water thoroughly, this way will remove any left over chemicals and is would not effect your results, remove the excess water.

· Fill the pipette with 25cm3 with the diluted HCl by placing a funnel on top and pouring slowly. This will avoid any spillage.

· Wash the volumetric flask with the solution of the calcium hydroxide to make sure that the flask is clean. Then pour out 40cm3 of calcium hydroxide into the volumetric flask.

· Add three drops of the methyl orange indicator to the limewater solution which is in the volumetric flask, the colour of the solution now should be slightly a light clear orange solution.

· Record the reading of the burette.

· Now release the solution of the HCl into the limewater solution slowly, observe the volumetric flask.

· When the solution turns from a light clear orange to a very light pink colour, this is an indication to stop and record the result. The white tile underneath the volumetric flask helps us with this because it gives us a better view of the colour change.

· If the solution has turned pink then this is an indication that we have over stepped the end point and the titration is not valid.

· By reading off the side of the burette what volume is left and taking this away from the starting volume (which should be 50ml) will give you the volume of acid required to neutralise the alkali. However since this is not accurate enough and anomalies do occur the test must be performed a further 3 times for any accurate results to become apparent. Each time you make a reading you must be careful to note the starting volume of acid in the burette and the end volume making sure there are no parallax errors.

Course work 4

Background Knowledge: Limewater solution is a clear coloured saturated Ca(OH)2(aq) is produced when calcium carbonate (Limestone) is decomposed to form calcium oxide CaO. Water is then added to this to form CaO (a.k.a quicklime), to produce slaked lime. Again, excess water is added to form Ca(OH)2(aq), limewater. Limewater, which is an alkali is used principally in medicine as an antacid as a neutralizer for acidic poisoning or treatment of burns. The concentration of a substance is the density of hydrogen ions in a solution, and is measured by the pH scale. Limewater as an alkali would have a ph of 9 - 14.

Objective: I am trying to find out the concentration of a limewater solution, containing 1gdm-3, by neutralising it with hydrochloric acid.

Method:

Apparatus -

· 5cm3 Pipette & pipette filler

· Burette & burette funnel

· Conical flasks

· Clamp & boss stand

· White tile

· Standardised volumetric flask

Chemicals -

· 250cm3 of limewater containing approx. 1gdm-3 of calcium hydroxide

· 2.00 moldm-3 of hydrochloric acid

· Distilled water e.g. Methyl orange

Ca(OH)2(aq) + 2HCl(l) CaCl2(aq) + 2H2O(l)

Firstly I will need to dilute the concentration of the HCl, because it is too concentrated. I will do this by using the pipette and the filler. I will fill a 2.5cm3 pipette full of hydrochloric acid, and place this in the standardised volumetric flask and fill to the mark with 247.5cm3 of distilled water. This makes the concentration 0.02moldm-3, and I will use this volume instead of 0.2moldm-3 or 2.0moldm-3 because it uses larger volumes in the titration giving less error. To find out the concentration in gdm-3 I will need to work out the concentration of the limewater in moldm-3 and multiply this by the R.F.M of limewater, which is (40 + 32 + 2) 74 amu. I will now need to titrate the hydrochloric acid against the limewater. I will fill the burette with HCl using the burette funnel (not necessarily to the top) but remember not to fill the burette above eye level, and remember to take the funnel out after it has been filled. Get a conical flask and fill it with 25cm3 of limewater using the pipette and pipette filler. Place roughly five drops of the methyl orange indicator into the conical flask. Methyl orange is used because it would produce a rapid colour change from orange to pink due to the nature of the strong acid and weak base. Clamp the burette above the conical flask, which should be on top of the white tile, so that there is an obvious colour change recognition. Firstly do a rough titration followed by three more accurate titrations, where you drip the HCL into the limewater when close to neutralisation. Record your results and do an average of the accurate three titration's and NOT the rough titration. you must carry out the experiment until concurrent results are obtained. For fast but accurate titrations, once you have a rough idea of how much HCl is needed, on the next go, you can release the HCl to free flow into the conical flask until you are near the total volume it took to neutralise it. You must constantly shake the conical flask throughout the titration because the methyl orange may turn pink, but it may not be permanent, and so you must keep titrating it until the first permanent pink colour change has been reached. Once you have recorded the volume, you are ready to start the calculations…

This shows how the apparatus should be set up.

Calculations:

Once you have found the average volume needed to neutralise the limewater, use the formula: Moles = Concentration x Volume to work out the number of moles present. Using the mole ratio of 1 : 2, divide this moles calculation by 2, to get the number of moles present in the limewater. Because you now know the moles and the volume of limewater used, you can work out the concentration of the limewater using the formula: Concentration = Moles / Volume. Now that you have the concentration, you can multiply this by ten (because we used one tenth of the limewater solution) and then by the R.F.M (74amu) to get the concentration in gdm-3.

Accuracy: The burette is +/- 0.1 cm-3. For example, if your volume you used to neutralise the limewater was 17.5cm-3, the error would be 17.5cm-3+/-0.1, giving an error of 0.57%, which is very accurate. When near neutralisation, you must drip the HCl into the conical flask so that you can obtain accurate results. The pipette used had an error margin of 0.6cm3.

Precision: You will need to repeat the titration roughly three times till you have concurrent results that are precise.

Safety:

· Never fill the burette above eye level.

· Always wear goggles and a lab coat.

· The burette must not be slanted at all in case of an imbalance.

· Never use a measuring cylinder or teat pipette to measure volumes as they are very inaccurate.

· If you find it difficult to read the burette, put a white piece of paper behind it when taking readings.

· When using a pipette filler, do not push the pipette end to hard into the filler because it easily liable to break.

Bibliography:

·  SEARCH + LIMEWATER

· Encarta encyclopaedia 2000 CD rom

· Chemistry 1 OCR

Course work 5 

The object of my experiment will be to determine the concentration of a given lime water solution that contains approximately 1g dm¯³ of calcium hydroxide.

The object of my experiment will be to determine the concentration of a given lime water solution that contains approximately 1g dm¯³ of calcium hydroxide.

 

Planning

The object of my experiment will be to determine the concentration of a given lime water solution that contains approximately 1g dm¯³ of calcium hydroxide.

I think it is always important to have some background knowledge about the chemical one is investigating :

Lime water is prepared by the following process,

1 > the thermal decomposition of calcium carbonate produces calcium oxide and carbon dioxide

CaCO3(s) ----> CaO(s) + CO2(g)

2 > next the calcium oxide is dissolved in water and calcium hydroxide forms

CaO(s) + H2O(l) ----> Ca(OH)2(s)

3 > further addition of water to calcium hydroxide provides lime water

The reaction I will be looking at for my experiment however, will be the one between limewater (Ca(OH)2) and hydrochloric acid (HCl):

Ca(OH)2(aq) + 2HCl(aq) ----> CaCl2(aq) + 2H2O(l)

This reaction follows the basic acid and alkali neutralisation reaction:

Alkali + Acid ----> Salt + Water

Due to the fact that this is a neutralisation reaction I shall need an indicator to see when the reaction end point is reached. Each indicator has its own range and it is important to pick an indicator that's colour change range coincides with the end point of the given experiment. As limewater is a fairly weak alkali and hydrochloric acid a strong acid, methyl orange will act as a suitable indicator as it changes colour in the pH range of 3.2 - 4.4.

METHYL ORANGE:

Low pH High pH

Red Yellow

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To carry out my experiments I shall need the following equipment / chemicals:

1 > Limewater ( 250 cm³ with approximately 1 g dm¯³ of calcium hydroxide )

2 > Hydrochloric acid ( 20 cm³ / 2.00 mol dm¯³ )

to act as basis for hydrochloric acid dilution

3 > Distilled water ( 500 cm³ )

to make up dilution of hydrochloric acid

4 > Indicator (methyl orange)

to see when reaction has reached its end point

5 > Pipette 25cm³

see fair test

6 > Volumetric flask 500cm³

used for making up dilution of HCl.

7 > Conical flask 250cm³

8 > Burette

9 > Clamp and stand

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Before carrying out any experiments it is always important to consider any necessary safety precautions:

RISK ASSESSMENT:

REACTANTS:

1 : Calcium Hydroxide :

In high concentrations of the powder form calcium hydroxide is corrosive to the eyes and skin, an irritation to the respiratory system and harmful if ingested. The concentration of calcium hydroxide in limewater however is very low and since it is in solution, practically harmless.

2 : Hydrochloric Acid :

HCl is an irritant at 2M or greater concentration and may cause irritation to skin and eyes if contact occurs. HCl also releases fumes if left to stand which can cause irritation to the respiratory system.

PRODUCTS :

1 : Anhydrous Calcium Chloride :

CaCl2 is classified as an irritant and will irritate the skin and eyes.

2 : Water :

No risk.

Due to the above chemicals being involved I have to take certain steps to ensure a safe practical, these include :

1 > wearing a lab coat - protecting my clothing and skin

2 > wearing safety goggles - protecting my eyes

3 > wearing gloves - protecting my skin (hands)

4 > making floor around work area is clear so there is nothing to trip / fall over

5 > making sure work area is well ventilated

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Method :

Firstly a suitable dilution of HCl needs to be made. I have decided on 0.1 mol dm⁻³ solution.

This can be done by:

1 > Adding the 20 cm³ of 2M HCl to the volumetric flask.

2 > Adding 380 cm³ of distilled water.

The meniscus of the solution should now be level with the 400 cm³ mark on the volumetric flask.

Doing the experiment :

1 > Set up burette with clamp and stand.

2 > Fill burette with 0.1 mol dm⁻³ HCl.

3 > Pipette 25 cm³ of the limewater solution into the conical flask.

4 > Add 5 drops of methyl orange to the limewater.

5 > Start the titration

6 > When colour change occurs, record the amount of HCl needed.

7 > Repeat experiment until concordant results are achieved, but do not repeat more than 5 times. If no concordant results are found, find a mean for the recorded values.

Results will be recorded in a table such as this:

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Finally one has consider measures to provide the experiment with the greatest amount of accuracy achievable:

1 > Accurate and Reliable Equipment :

I chose a pipette and volumetric flask as they are far more accurate in measuring liquids than for example syringes, measuring cylinders and normal beakers. This ensures better overall accuracy.

2 > Double checking :

Human error is usually one of the greatest sources of inaccuracy, to try and keep this to a minimum I will double check all of my results and remember to perform standard procedures like holding my eye in line with the meniscus to avoid the parallax error.

3 > Repeating experiments :

This allows for anomalous results to be excluded and results to be more accurate.

4 > Letting the HCl drip out of the burette slowly so that time of colour change can be more accurately pinpointed.

5 > All the tests will be carried out at room temperature and pressure.

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BIBLIOGRAPHY:

1:

Chemistry 1

Chapter 5 - Group II elements and their chemistry

Chapter 14 - Reaction Rates

Brian Ratcliff, Helen Eccles, David Johnson, John Nicholson and John Raffan

© Cambridge University Press

2:

Chemistry 2

Chapter 14 - Acids, Bases and Buffers

Brian Ratcliff and Helen Eccles

© Cambridge University Press

3:

http://www.osha-slc.gov

4:

http://www.ilo.org

5:

http://www.essaybank.co.uk/free_coursework/1291.html